Illumination source and method therefor

ABSTRACT

An illumination source and a method therefor. A light source includes a light circuit configured to process light and direct light, and a lighting element optically coupled to the light circuit to provide multiple colors of light. The light circuit propagates light using light guides. The use of light guides eliminates the use of free space optical elements, enabling the creation of more compact light sources. Furthermore, the use of light guides may enable the creation of light sources with fewer mechanical restrictions, thereby making the light sources potentially more reliable and less expensive.

This application is a divisional of application Ser. No. 11/765,941,filed Jun. 20, 2007.

TECHNICAL FIELD

The present invention relates generally to a system and method fordisplaying images, and more particularly to an illumination source and amethod therefor.

BACKGROUND

A typical illumination source for a display system makes use of one ormore light sources that may include electric arc lamps, light emittingdiodes, lasers, and other forms of solid-state lights, and so forth, toprovide needed light. The light may be used to project an image createdby a microdisplay, for example, onto a display plane. A digitalmicromirror device (DMD), one type of microdisplay, contains a largenumber of micromirrors that may individually pivot between an on stateand an off state depending on an image being displayed, reflecting thelight either onto or away from the display plane. The DMD, controllingthe light reflected onto and away from the display plane, creates aprojection of the image on the display plane.

The light from the light sources may be combined using beam shaping freespace optics and dichroic technology. For example, optical lenses,filters, gratings, beam splitters, and so forth, may be used to focus,collimate, combine, split, filter, and otherwise process or manipulatethe light from the light sources into a condition suitable for use in adisplay system.

The use of free space optics and dichroic technology has enabled fullyoperable illumination sources. However, with a continued push forsmaller display systems, even pocket-sized display systems, the physicalsize of illumination sources using free space optics and dichroictechnology may hamper the development of extremely small displaysystems.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by embodiments of anillumination source and a method therefor.

In accordance with an embodiment, a light source is provided. The lightsource includes a light circuit and a lighting element optically coupledto the light circuit. The light circuit processes light and propagateslight using light guides. The lighting element provides multiple colorsof light.

In accordance with another embodiment, a display system is provided. Thedisplay system includes a monolithic light source to produce light, alight modulator optically coupled to the monolithic light source andpositioned in a light path of the monolithic light source after themonolithic light source, and a controller electronically coupled to thelight modulator and to the monolithic light source. The light modulatorproduces images on a display plane by modulating light from themonolithic light source based on image data, and the controller issuesmodulator commands to the light modulator based on the image data. Themonolithic light source includes a lighting element that providesmultiple colors of light, and a light circuit. The light circuitincludes optical processing elements that manipulate the multiple colorsof light, and light guides coupled to the optical processing elementsand to the lighting element, wherein the light guides propagate light.

In accordance with another embodiment, a method of manufacturing adisplay system is provided. The method includes installing a monolithiclight source, installing an optics system optically coupled to themonolithic light source and in a light path of the monolithic lightsource, installing a microdisplay optically coupled to the optics systemand in the light path after the optics system, and installing acontroller electrically coupled to the microdisplay. The monolithiclight source comprises light guides to internally propagate light.

An advantage of an embodiment is that the illumination source may bemade small due to a reduction (or elimination) in the use of free spaceoptics and dichroic technology, such as large optical lenses, filters,gratings, and so forth.

A further advantage of an embodiment is a reduction in mechanicaltolerances and the continued maintenance of illumination sources haslargely been eliminated. Generally, for example, there are no largeoptical lenses to be knocked out of alignment, mechanical devices towear out, and so forth.

Yet another advantage of an embodiment is that the manufacture of theillumination sources has been simplified due to the elimination of manyassembly steps. Furthermore, many mechanical tolerances have beenremoved. Therefore, the illumination sources may become significantlyless expensive.

Another advantage of an embodiment is that many optical managementrequirements of an illumination system, such as modulation, specklereduction, color combination, and so on, may be integrated into a singlesubstrate. This may allow wafer fabrication techniques to be applied,leading to further cost reductions.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the embodiments that follow may be better understood.Additional features and advantages of the embodiments will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 a is a diagram of a projection display system;

FIG. 1 b is a diagram of a flying spot display system;

FIG. 2 a is a diagram of a monolithic light source;

FIGS. 2 b through 2 d are diagrams of alternate light elements;

FIGS. 3 a and 3 b are diagrams of single optical grating systems forcombining different wavelengths of light;

FIG. 4 is a diagram of a monolithic light source utilizing opticalfiber;

FIG. 5 is a diagram of a monolithic light source with light modulationfunctionality;

FIG. 6 is a diagram of a portion of a monolithic light source used forspeckle reduction; and

FIGS. 7 a through 7 c are diagrams of sequences of events in themanufacture of a display system.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments are discussed in detail below.It should be appreciated, however, that the present invention providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative of specific ways to make and use the invention, anddo not limit the scope of the invention.

The embodiments will be described in a specific context, namely a laserillumination source for use in a DMD-based display system. The inventionmay also be applied, however, to illumination sources using other formsof illumination, such as electric arc lamp, light emitting diode andother solid-state light sources, as well as other forms of coherentlight. The illumination source may be used in other forms of displaysystems, such as those utilizing transmissive or reflective liquidcrystal displays, liquid crystal on silicon, ferroelectricliquid-crystal-on-silicon, deformable micromirrors, and other forms ofmicrodisplays and spatial light modulators. Furthermore, theillumination source may be used in applications wherein there is a needfor a well controlled source of light. For example, the illuminationsource may be used in a flying spot display, wherein images may becreated on a display screen using a high-energy light beam, such as alaser, with each pixel represented by a narrow pulse of light or lack oflight, in each specific location.

With reference now to FIG. 1 a, there is shown a high-level diagramillustrating an exemplary DMD-based projection display system 100. TheDMD-based projection display system 100 includes a DMD 105 thatmodulates light produced by a light source 110. The DMD 105 is anexample of a microdisplay or an array of light modulators. Otherexamples of microdisplays may include transmissive or reflective liquidcrystal, liquid crystal on silicon, ferroelectricliquid-crystal-on-silicon, deformable micromirrors, and so forth. In amicrodisplay, a number of light modulators may be arranged in arectangular, square, diamond shaped, and so on, array.

Each light modulator in the microdisplay may operate in conjunction withthe other light modulators in the microdisplay to modulate the lightproduced by the light source 110. The light modulated by the DMD 105 maybe used to create images on a display plane 115. The DMD-basedprojection display system 100 also includes an optics system 120, whichmay be used to collimate the light produced by the light source 110 aswell as to collect stray light, and a lens system 125, which may be usedto manipulate (for example, focus) the light reflecting off the DMD 105.

The DMD 105 may be coupled to a controller 130, which may be responsiblefor loading image data into the DMD 105, controlling the operation ofthe DMD 105, providing micromirror control commands to the DMD 105,controlling the light produced by the light source 110, and so forth. Amemory 135, which may be coupled to the DMD 105 and the controller 130,may be used to store the image data, as well as configuration data,color correction data, and so forth.

FIG. 1 b illustrates an exemplary flying spot display system 150. In theflying spot display system 150, a scanning mirror 155, operating as alight modulator, may rapidly move about two axes to scan light from thelight source 110 onto the display plane 115. The scanning mirror 155 maycomprise a single mirror that may be capable of movement along two axesor two mirrors, each capable of movement along one of the two axes.Typically, the axes may be orthogonal. The light from the light source110 may be time modulated to create individual pixels and a viewer'seyes may integrate the light on the display plane 115 to create animage. A controller 160 may be used to control the scanning of thescanning mirror 155 as well as a modulation of the light source 110. Thecontroller 160 may control the scanning of the scanning mirror 155 byissuing modulator control commands as well as the modulation of thelight source 110. Both the control of the scanning mirror 155 and thelight source 110 may be based on the image data. A flying spot displayoperates in a manner similar to a cathode-ray tube display, with beamsof electrons are scanned over a phosphor coated display plane ratherthan a light beam scanned over a display plane.

FIG. 2 a illustrates a monolithic light source 200. The light source 200may be used to provide a collimated white light. The light source 200comprises a planar lightwave circuit 204 (PLC) fabricated on a substrate205. The PLC 204 is a form of light circuit formed on the substrate 205.The substrate 205 may be formed from lithium niobate (LiNbO₃). Inaddition to lithium niobate, other materials may be used to form thesubstrate, including magnesium oxide doped lithium niobate (MgO:LiNbO₃),zinc oxide doped lithium niobate (ZnO:LiNbO₃), iron doped lithiumniobate (Fe:LiNbO₃), and combinations thereof. Other types of materialsthat may be used to form the substrate may include: lithium tantalite(LTA), lithium triborate (LBO), beta-barium borate (BBO), potassiumtitanyl phosphate (KTP), and combinations thereof.

It may be possible to locally dope the substrate 205 with ions such asmagnesium (Mg), iron (Fe), zinc (Zn), hafnium (Hf), copper (Cu),gadolinium (Gd), erbium (Er), yttrium (Y), manganese (Mn) and boron (B)to increase the index of refraction of the substrate and createwaveguides, such as waveguides 210-214. It may also be possible todirectly pattern the waveguides 210-214 onto the substrate 205. Forexample, the waveguides 210-214 may be patterned onto the substrate 205by techniques such as etching, photolithography, doping, and so forth.Additionally, the use of a photonic crystal lattice may yield similarlyperforming waveguides.

Light from lasers 215-217 may be coupled into the waveguides 210-212 onthe substrate 205 by couplers 220-222. The lasers 215-217 may eachproduce light at a different wavelength. For example, laser 215 mayproduce light in a red wavelength, laser 216 may produce light in agreen wavelength, and laser 217 may produce light in a blue wavelength.Although shown to include three lasers, the light source 200 may combinelight for any number of lasers. For example, the light source 200 maycombine light from two, four, five, six, and so forth, lasers.Additionally, other light sources may be used in place of lasers. FIGS.2 b through 2 d illustrate portions of alternate light sources, such aslight emitting diodes or some other form of solid-state light source,electric arc lamps, and so on, may be used in place of lasers. Lightfrom the light emitting diodes, solid-state light source, electric arclamp, and so forth, may be coupled into the PLC 204 by the coupler 220.Therefore, the illustration and discussion of three lasers should not beconstrued as being limiting to either the scope or the spirit of thepresent invention. The couplers 220-222 may be butt-couplers or spherelenses, for example.

A coupler 225 may be used to combine (process or manipulate) light fromthe laser 215 with light from the laser 216 and a coupler 226 may beused to combine light from the laser 217 with the combined light fromthe lasers 215 and 216. The couplers 225 and 226, when created on thesubstrate 205, may be examples of integrated light processing elements.Examples of the couplers 225 and 226 may be couplers that areBragg-based or Fabry-Perot-based. Additionally, common integrateddichroic couplers that may have been tuned to couple light from a firstwaveguide to a second waveguide using evanescent waves may also be usedas couplers 225 and 226. The couplers 225-226 may be tuned so that aninteraction length may be set to enable a total transfer of light of aspecific wavelength from a first waveguide to a second waveguide and maybe used to combine light from the lasers 215-216. Other examples oflight processing performed by the PLC 204 (a light circuit) may befiltering, focusing, scattering, diffusing, splitting, combining, and soon.

The couplers 225 and 226 may be formed on the substrate 205 by localdoping of the substrate 205. The doping of the substrate 205 may beperformed utilizing the materials used to create the waveguides, and mayinclude ions such as magnesium (Mg), iron (Fe), zinc (Zn), hafnium (Hf),copper (Cu), gadolinium (Gd), erbium (Er), yttrium (Y), manganese (Mn)and boron (B). The couplers 225 and 226 may also be formed byalternating different materials including the different substratematerials including lithium niobate (LiNbO₃), magnesium oxide dopedlithium niobate (MgO:LiNbO₃), zinc oxide doped lithium niobate(ZnO:LiNbO₃), iron doped lithium niobate (Fe:LiNbO₃), lithium tantalite(LTA), lithium triborate (LBO), beta-barium borate (BBO), potassiumtitanyl phosphate (KTP), and combinations thereof along the waveguides210-213. Air, vacuum, and a variety of gasses may also be used in thecouplers 225 and 226. Slices of waveguide material may be removed,leaving a gap (gaps) to be filled with air, vacuum, various gasses, andso forth, to function as a waveguide. Additionally, creating periodicstress on the waveguides 210-213 may also be used to form couplers.Bragg-based and Fabry-Perot-based couplers as well as the othertechniques discussed herein are considered to be well understood bythose of ordinary skill in the art of the present invention.

Light output from the coupler 226, traveling in the waveguide 214, maythen exit the substrate 205 and be provided to a lens 230. The lens 230may be used to collimate the light, forming a collimated white light235. The lens 230 may be a graded index (GRIN) lens or an aspheric lens,for example. The lens 230 and the waveguide 214 may be butt-coupledtogether using an index matching material. Alternatively, anantireflective coating (AR) may be applied to the end of the waveguide214 and the lens 230 may then be butt-coupled to the waveguide 214.Another technique may involve the use of an optical fiber coupled at oneend to the waveguide 214 and then the lens 230 may be attached to theoptical fiber at another end.

Since the waveguides 210-214 and the couplers 225 and 226 may be formedin the substrate 205 or on the substrate 205, they may be less sensitiveto misalignment than comparable free space optics and dichroic elements.Additionally, the couplers 225 and 226 may be made smaller in size thancomparable free space elements, thereby enabling the light source 200 tobe smaller than a similar light source utilizing free space opticalelements. Furthermore, since light from the lasers 215-217 arepropagating in the waveguides 210-214 and may not disperse to the extentthat they may when propagating in free space, the amount of light lossin the light source 200 due to light dispersion may be less than asimilar light source utilizing free space optical elements. Theseadvantages and others may yield a light source that may be smaller, morerobust, and brighter than a similar light source utilizing free spaceoptical elements.

The monolithic light source 200 may be constructed so that the lasers215-217 and the couplers 220-222, along with other elements, are placedon a board, a circuit board, a circuit module, and so forth, with thesubstrate 205. The combination of the lasers 215-217, the couplers220-222, and the substrate 205 on a board may create a single monolithicentity that may help to improve the reliability of the light source 200by reducing susceptibility to shock and vibration while potentiallyreducing mechanical manufacturing tolerances. In another embodiment, thelasers 215-217 and the couplers 220-222 may be fabricated on thesubstrate 205 along side the discrete optical components and waveguides.

FIGS. 3 a and 3 b illustrate diagrams of single optical grating systemsfor combining different wavelengths of light. FIG. 3 a illustrates asingle optical grating system 300 with a reflective grating. In thesingle optical grating system 300, light beams 305-307 of differentwavelengths of light may be incident on a lens 310. The lens 310 may bean aspherical lens or a GRIN lens, for example. After traversing thelens 310, the light beams 305-307 traverse free space and reflect off areflective grating 315. The reflective grating 315 may effectivelycombine the light beams 305-307 into a single beam 320 that traversesback through the lens 310, exiting the lens 310 as a collimated whitelight beam 325.

Similarly, a single optical grating system 350 shown in FIG. 3 b maymake use of a transmission grating to produce collimated white light.Light beams 305-307 traverse through a lens 355, which may be similar tothe lens 310, and as the light beams 305-307 exit the lens 355, theybecome incident to a transmission grating 360. As the light beams305-307 pass through the transmission grating 360, they may be combinedinto a single beam 365 of collimated white light.

In the light source 200 fabricated as a PLC, optical elements such asthe waveguides 210-214 and the couplers 225 and 226, may be fabricateddirectly on the substrate 205. This may be analogous to an integratedcircuit, wherein multiple circuit elements are fabricated on asubstrate. It may also be possible to implement a similar light sourceutilizing discrete optical components. FIG. 4 illustrates a light source400 created using discrete optical components. Optical fiber 405 mayfunction as waveguides for light from lasers 410 that may be coupledinto the optical fiber 405 via couplers 415. The optical fiber 405 maybe used as optical interconnects between discrete optical elements, suchas couplers 420 and a lens 425. The couplers 420 may be discreteimplementations of Bragg-based and Fabry-Perot-based couplers and may beused to combine light at their respective inputs, while the lens 425 maybe a GRIN lens and may create a collimated white light beam 430 from acombination of light from the lasers 410. The optical elements, such ascouplers 420 and lens 425, as well as the optical fiber 405 may bemounted on a backer board, a printed circuit board, or so forth, toprovide mechanical stability for the light source 400. Collectively, thediscrete optical elements, such as couplers 420, and the optical fiber405, along with the board, circuit board, backer board, circuit module,and so forth, may form a light circuit 404. The light source 400 may beformed into a monolithic light source by attaching the discrete opticalcomponents, such as the couplers 420, the optical fiber 405, as well asthe lasers 410 and the couplers 415 to a board, a circuit board, acircuit module, or so on.

A light source, fabricated as a PLC, may also include functionalitybeyond producing collimated white light. FIG. 5 illustrates a monolithiclight source 500 fabricated on a substrate 205 with a capability tomodulate light. The light source 500 includes a waveguide 505functioning to direct light, from lasers 510, for example, and coupledinto the waveguide 505 with a coupler 515, between various integratedoptical elements. A coupler 520, such as a Bragg-based orFabry-Perot-based coupler, may be used to combine multiple light beamsinto a single light beam. Furthermore, coupling via evanescent waves mayalso be used. If the light source 500 were to be created using discreteoptical elements and fiber optics, then a fused bi-conical taper (FBT)coupler may be used.

A modulator 525 may be used to modulate light from the laser 510. Themodulator 525 may be a Mach-Zender interferometer and may be used tomodulate light at one of several inputs to the modulator 525. Themodulator 525, when created on the substrate 205, may be examples ofintegrated light processing elements. In addition to the Mach-Zenderinterferometer, other techniques may be employed to modulate lightproduced by the laser 510, including a switchable Bragg grating, avariable coupler, a Pockel cell, and so forth. The modulator 525 mayeffectively switch the light from the laser 510 on or off as desired, byadding a 180 degrees out-of-phase version of a light wave to itself, forexample. Therefore, a light beam 530 may be a light beam without lightfrom one or more of the lasers 510. For example, to produce a light beamwith purely one color of light, light from the other two lasers of thelight source 500 may be eliminated by respective modulators 525.

FIG. 6 illustrates a speckle reduction circuit 605 of a light source600, wherein the light source 600 and the speckle reduction circuit 605may be fabricated on a substrate 205. The speckle reduction circuit 605may be located at an output end of the light source 600, prior to anoutput light exiting the light source 600, for example. The specklereduction circuit 605 includes a waveguide 610 that may be split into aplurality of separate waveguides, such as waveguide 611 and waveguide612. The waveguides may then be passed through a set of electrodes. Whenan electric potential is applied across the electrodes, an electricfield may be generated that may modify the material's refractive index.This may alter a delay in the light, creating a phase shift. Eachelectrode may impart a random phase shift (truly random, pseudo-random,periodic with different periods, and so forth) on light carried withinthe waveguide passing through the electrode. For example, electrode 616may impart a first random phase shift on the light carried in thewaveguide 612. Similarly, electrode 615 may impart a second random phaseshift. Preferably, a random phase shift imparted by an electrode shouldhave no relationship with the random phase shifts imparted by otherelectrodes. The electrodes, when created on the substrate 205, may beexamples of integrated light processing elements.

Waveguides leading from the electrodes, such as waveguides 620 and 621,may then provide the light to a lens 625, such as a GRIN lens. Outputfrom the lens 625 may be a set of multiple beams of light, such as beam630 and beam 631, with the light beams having different phase angles anda random phase relationship.

In addition to collimation, light modulation, and speckle reduction, alight source fabricated using a PLC may also be used to convert alight's wavelength. For example, it may be possible to convert infrared(IR) light to visible light. Visible light in a variety of colors may beprovided to a PLC and may be combined with visible light generated froman IR light located on the PLC. A non-linear substrate, such as one madefrom lithium niobate (LNB), lithium tantalite (LTA), lithium triborate(LBO), beta-barium borate (BBO), potassium titanyl phosphate (KTP), andcombinations thereof, may be used to perform non-linear operations on anIR light beam on the PLC. Examples of such operations may include secondharmonic generation (SHG), sum frequency generation (SFG), differencefrequency generation (DFG), parametric amplification and parametricoscillation by patterning waveguides, periodically or quasi-periodicallypoled structures, optical parametric oscillators (OPO), opticalparametric amplifiers (OPA), and so forth. The non-linear operations maybe used to generate any color or any set of colors of light desired,such as red, green, and/or blue.

FIG. 7 a illustrates a sequence of events 700 in the manufacture of anexemplary display system with monolithic light source. The manufactureof the display system may begin with installing a monolithic lightsource (for example, the light source 200 fabricated on a PLC, or thelight source 400 installed on a backer board or circuit board), whichmay produce multiple colors of light (block 705). The manufacture maycontinue with installing a microdisplay, for example, DMD 105 (block710) in the light path of the multiple colors of light produced by thelight source (block 705). A lens and/or optics system, such as theoptics system 120 and the lens system 125 may next be installed (block715). A controller, such as the controller 130, for the display systemmay then be installed in the light path of the multiple colors of light(block 720). Finally, a display plane, such as display plane 115, may beinstalled (block 725). The order of the events in this sequence may bechanged, the sequence may be performed in a different order, or some ofthe steps may be performed at the same time to meet particularmanufacturing requirements of the various embodiments of the DMD, forexample.

The installation of the monolithic light source, block 705, may differdepending on the type of light source being installed. FIG. 7 billustrates the installation of a light source fabricated from a PLC.The installation may include the installation of a PLC that containsoptical elements such as waveguides and optical processing elements(block 765) and light sources, such as lasers, light emitting diodes,and so forth (block 760). FIG. 7 c illustrates the installation of alight source containing discrete optical elements. The installation mayinclude the installation of discrete optical elements (block 770), andlight sources, such as lasers, light emitting diodes, and so forth(block 775) on the back board or circuit board, and then optical fiberto connect the light sources to the discrete optical elements (block780).

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

1. A display system comprising: a monolithic light source to producelight, the monolithic light source comprising, a lighting element toprovide multiple colors of light, and a light circuit comprising,optical processing elements configured to manipulate the multiple colorsof light, and light guides coupled to the optical processing elementsand to the lighting element, the light guides to propagate light; alight modulator optically coupled to the monolithic light source andpositioned in a light path of the monolithic light source after themonolithic light source, the light modulator configured to produceimages on a display plane by modulating light from the monolithic lightsource based on image data; and a controller electronically coupled tothe light modulator and to the monolithic light source, the controllerconfigured to issue modulator commands to the light modulator based onthe image data.
 2. The display system of claim 1, wherein the lightcircuit comprises optical processing elements and light guidesintegrated on a substrate.
 3. The display system of claim 1, wherein thelight circuit comprises discrete optical processing elements placed on acircuit board, and wherein the light guides comprise optical fibers. 4.The display system of claim 1, wherein the light modulator is selectedfrom the group consisting of: digital micromirror device, transmissiveor reflective liquid crystal display, liquid crystal on silicon,ferroelectric liquid-crystal-on-silicon, deformable micromirror,scanning mirror, and combinations thereof.